a. Field of the Invention
The present invention pertains generally to integrated circuit design and manufacturing, and more specifically to software and database techniques that aid in analyzing an electrical circuit that is intended to be manufactured as an integrated circuit.
b. Description of the Background
The process of creating an integrated circuit begins by first designing an electrical schematic of an electrical circuit that will someday be created as an integrated circuit. Until the electrical circuit schematic is designed, the layout of the integrated circuit cannot begin. To make circuit design more efficient and less prone to error, software tools have been created to assist in creating the electrical circuit schematic drawing. The software tool, commonly called electrical schematic capture software, allows an electrical circuit designer to create an electrical circuit schematic in much the same manner as computer aided design (CAD) software tools assist a mechanical draftsperson in creating a mechanical drawing of a physical device. Some of the most common electrical schematic capture software tool vendors include: Mentor Graphics Corporation, Cadence Design Systems, and Synopsys, Inc. Many of the electrical schematic capture software tool vendors also supply electrical circuit analysis and simulation software tools, and integrated circuit layout and testing software tools. Mentor Graphics Corporation is located at 8005 SW Boeckman Road, Wilsonville, Oreg. 97070, and may be contacted at phone numbers 800-592-2210 and 503-685-7000, or on the Internet at www.mentor.com. Cadence Design Systems is located at 2655 Seely Avenue, San Jose, Calif. 95134, and may be contacted at phone number 408-943-1234, or on the Internet at www.cadence.com. Synopsys, Inc. is located at 700 East Middlefield Road, Mountain View, Calif. 94043, and may be contacted at phone numbers 650-584-5000 and 800-541-7737, or on the Internet at www.synopsys.com.
The electrical circuit designer typically lays out an electrical circuit schematic by placing primitive electrical devices onto an electrical schematic page. The electrical circuit designer then connects the primitive electrical devices with a line in a manner that creates the desired electrical circuit. The line represents an electrically connecting wire, or an electrical short, between the connected primitive electrical devices. A primitive electrical device is a basic electrical device that cannot be broken down into smaller devices within the electrical schematic capture software. The primitive electrical device is typically a device such as a resistor, capacitor, inductor, diode, transistor, and other similar basic electrical devices. The attributes, or properties, of each primitive electrical device are specified by the electrical circuit designer, and stored within the electrical schematic capture software. The device attributes determine the type and characteristics of each primitive electrical device within the system. For instance, a resistor might have attributes to define resistance, power ratings, and electrical connection points. Other primitive electrical devices would have similar, appropriate attributes to define the electrical characteristics for the primitive electrical device.
Many times, an electrical circuit designer may want to reuse a part of a circuit, sometimes called a sub-circuit, in other sections of the overall circuit. This is accomplished within the electrical schematic software tool by defining a sub-circuit as a macro. The macro has macro attributes similar to the primitive electrical device that define the external electrical connection points for the macro. The makeup of the internal electrical devices determine the electrical behavior of the macro. A macro can be made up of other macros defined within the electrical schematic capture software tool, as well as primitive electrical devices.
After the electrical circuit schematic is completed, the electrical circuit represented by the electrical circuit schematic is simulated to insure the electrical circuit functions as desired by the circuit designer. The simulation of the electrical circuit may be performed by the electrical schematic capture software tool, or by another analysis software tool. The choice of using the electrical schematic capture software tool simulation or an external simulation software tool depends on the complexity of the electrical circuit, and the complexity of the desired simulation. In order to allow an external software tool to analyze the electrical circuit, the electrical schematic software tool has the ability to create a netlist text file representing the electrical circuit in a text form. The netlist text file contains all of the data defining the primitive electrical devices, the electrical attributes of each primitive electrical device, the sub-circuit macros, the electrical attributes of each macro, the electrical connections for all of the primitive electrical devices and macros, and the attributes of each electrical connection including the connection point of each primitive electrical device and macro included in each electrical connection.
The netlist text file is imported by the external analysis software, and the electrical circuit is simulated. If errors in the electrical circuit are found, changes are made to the electrical circuit schematic in the electrical schematic software package. The netlist text file for the updated electrical circuit schematic is created and imported into the analysis software. The simulation and circuit schematic modification is repeated until the electrical circuit functions as desired on the simulator. Many of the analysis software tools allow the user to make modifications to the circuit being simulated so that the analysis process is not too cumbersome.
Once the electrical circuit functions properly within the simulator, the electrical circuit must then be created as an integrated circuit. The same netlist text file used to send electrical circuit data to external analysis and simulation software tools is used to export electrical circuit data to an integrated circuit layout software tool. The integrated circuit layout software tool imports the electrical circuit data in the netlist text file, and uses the electrical circuit data to layout the physical features of the integrated circuit that create the desired electrical circuit. After the integrated circuit layout is performed additional analysis and simulation of the integrated circuit is performed. The analysis and simulation of the integrated circuit allows the circuit designer to perform topological checks of the integrated circuit to find parasitics within the integrated circuit layout. A topological check may be configured to look for layout guidelines, known as Design Rule Checks (DRC's). For example, a topological check may look for a circuit element that has two MOSFET transistors connected together from the drain of one transistor to the gate of the other transistor, and where the source of each transistor is connected to a different ground plain. Since the ground plains may be at different electrical potentials there is a parasitic effect between the two transistors that may cause problems in the function of the circuit that would not be present in a simulation of the electrical circuit that does not include the physical integrated circuit layout. If problems are found during the analysis and simulation of the integrated circuit layout, the circuit changes are made using the electrical schematic capture software tool and the integrated circuit layout is performed again.
After a satisfactory analysis and simulation is performed on the integrated circuit layout, the integrated circuit is created and electrically tested for proper operation. If a problem is encountered, the electrical circuit schematic must be updated within the electrical schematic software tool, and the testing, simulation, layout, and manufacturing of the integrated circuit must be performed again to insure a properly functioning integrated circuit.
The present application is filed simultaneously with application Ser. No. 10/956,862, entitled “Netlist Database” by the present inventor, Eric Miller, filed Sep. 30, 2004, the full text of which is hereby specifically incorporated by reference for all it discloses and teaches.
A netlist database is an object oriented netlist database as disclosed in the above mentioned application Ser. No. 10/956,862, entitled “Netlist Database.” A netlist database stores electrical circuit data parsed from a netlist text. To obtain the netlist text file, an electrical circuit schematic of an electrical circuit is created using a commercially available electrical schematic capture software tool. The electrical schematic capture software tool is then directed to create the netlist text file that is representative of the electrical circuit. A netlist text file parser program first creates the object oriented netlist database structure, then parses the netlist text file, and finally fills the netlist database with objects that represent the electrical circuit data contained in the netlist text file.
Structured Query Language (SQL) is a computer language for reading and updating relational databases. SQL uses statements to perform instructions to create, read, change, or delete data in a relational database. A relational database is made up of tables. Each table contains records of an item of data. Each record holds data in predefined fields, or data elements. A typical query statement to retrieve data from a relational database consists of a syntax of the form of “SELECT field FROM table WHERE condition.” The “SELECT field” syntax specifies the field, or data element, of a record to obtain from the relational database table specified in the “FROM table” syntax. The “WHERE condition” syntax specifies a logical condition that must be met before a record is selected from the relational database “FROM table” for output into a query output sub-table. There is additional syntax for creating, changing, or deleting data within the relational database as well as more complex structures to allow more sophisticated searches of multiple tables, and sophisticated conditional logic for the “WHERE condition” syntax. SQL is a very common language used by many database programmers to access data in relational databases.
SQL is a non-proprietary (open) language with a language syntax set by several standards making bodies operating together. The standards bodies creating the SQL standard are the American National Standards Institute (ANSI), the International Organization for Standardization (ISO), and the International Electrotechnical Organization (IEC). The International Committee on Information Technology Standards (INCITS) is the joint committee in charge of the SQL standard. There are several versions of the SQL standard available for use by the public. The original SQL standard, ANSI X3.168-1989, is typically referred to as SQL 1. SQL 1 is the core definition of SQL, and most, if not all, of the SQL 1 standard is incorporated in later SQL standards. In fact, the second SQL standard revision, ANSI INCITS 135-1992 (formerly ANSI X3.135-1992, renamed in 1998), includes the entire SQL 1 standard. The second SQL standard revision is typically referred to as SQL 2. A third SQL standard revision is available under the name of INCITS/ISO/IEC 9075: 1999. The third SQL standard revision is typically called SQL 3. A forth SQL standard revision, INCITS/ISO/IEC 13249: 2003, has recently been released, but it has not been adopted by industry as completely as the older SQL revisions. All SQL revisions are available from ANSI at 11 West 42nd Street, New York, N.Y. 10036, or on the Internet at www.ansi.org.